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School of Food Science and Nutrition FACULTY OF MATHEMATICS AND PHYSICAL SCIENCES Ultrasonic Techniques for Fluids Characterization Malcolm J. W. Povey May 18 th to May 22 nd 2009

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Reproduction You may freely use this presentation. You may reproduce the material within on condition that you reference the original source(s). The author asserts his moral and paternity rights regarding the work.

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Welcome Welcome to the School of Food Science and Nutrition This course addresses the fundamental physical questions needed to understand a range of practical applications of ultrasound. Many of these applications have been developed here. There are no course pre-requisites, apart from an interest in ultrasound as a practical tool for the study of materials. Some of you may feel that I am teaching my grandmother to suck eggs. Please be patient, sucking eggs is not as easy as it looks. Not everyone knows how to do it.

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The Beginnings 1826, the first determination of the speed of sound in water http://en.wikipedia.org/wiki/Jacques_Charles_Fran%C3%A7ois_Sturm

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Metaphors Use light as a metaphor Here the suns rays are scattered from the back of the cloud, creating mini- images of the sun. The cloud absorbs the light, with darkness at the front and light at the back. These are called anti- crepuscular rays.

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Group and Phase velocity Group velocity Phase velocity is the speed of a given frequency component within the wave This is the velocity of the wave envelope k is called the wave number, λ is the wavelength e.g ocean waveswaves

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Velocity and attenuation Attenuation coefficient This is called the wave VECTOR because it comprises two numbers, the first one is sometimes called the real number and the second the imaginary, because it is multiplied by the square root of minus one.

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Impedance Z In words: The impedance is the ratio of the pressure change resulting during the passage of the wave to the particle velocity. This approximates to the product of the density times the speed of sound.

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Incoherence The wave front can break up like this due to diffraction and scattering. The transducer will not detect the wave front because the phase variation across the transducer face sums to zero.

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Underlying physics Conservation of momentum -Newtons second law, force is mass (m) times acceleration ( where v is velocity). Conservation of mass Together conservation of momentum and conservation of mass give rise to the Navier-Stokes equation for fluids. In soft solids an even more complicated relationship exists due to time dependent shear and compressibility. Conservation of energy Second law of thermodynamics

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1. Introduction 1.1 The Beginnings 1.2 Understanding Sound 1.3 Representations of Sound 1.4 Sounds Classical and Sounds Quantum 1.5 Comparisons between Light and Ultrasound 1.6 The Adiabatic Idealization 1.7 Common Sense is Unsound 1.8 Scope of This Work How to Use This Book